119 innovations

Non-explosive chemical fertilizer

The use of ammonium nitrate in IEDs is so widespread that the Joint Improvised Explosive Device Defeat Organization (JIEDDO) last year put out a call for ideas on ways to neutralize ammonium nitrate as an IED explosive. It’s a difficult task because its legal use is so common. Even though ammonium nitrate fertilizer is illegal in Afghanistan for example, it is easily sourced from neighboring Pakistan, where agriculture accounts for a quarter of the country’s gross domestic product.

Knowing that in ammonium nitrate the ammonium ion is weakly attracted to the nitrate ion, and that the right chemical reaction can pull them apart, researchers decided to look for a compound they would rather cling to that could be added to the ammonium nitrate. They tried several materials, including iron sulfate, a readily available compound discarded by the ton from steel foundries.

If someone attempts to alter the ammonium nitrate/iron sulfate mixture to make it detonable by mixing it with fuel, the iron ion takes the nitrate ion and the ammonium ion takes the sulfate ion. The result is that the iron sulfate becomes iron nitrate and the ammonium nitrate becomes ammonium sulfate, neither of which is detonable.

But the new compound wouldn’t be much use if it weren’t also a good fertilizer. Thankfully, it is. In fact, the addition of iron sulfate to the mix makes the new fertilizer even better than ammonium nitrate for alkaline soils.